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Home / DTC / P1651 — Power Steering Pressure Switch Input Fault

P1651 — Power Steering Pressure Switch Input Fault

Detailed page for trouble code P1651.

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Code

P1651

LINCOLN P — Powertrain

Power Steering Pressure Switch Input Fault

Brand: LINCOLN
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Faulty power steering pressure switch
  • Open, short or high-resistance wiring between switch and PCM
  • Corroded or loose connector/terminal at the switch or PCM
  • Low power steering fluid level or internal pump/valve failure reducing system pressure
  • Intermittent contact from damaged harness (chafing, pinched, broken wires)
  • Poor ground or reference voltage to the switch

Symptoms

  • Malfunction Indicator Lamp (MIL) or warning lamp illuminated
  • Power steering assist reduced or disabled (stiff/heavy steering)
  • Intermittent loss of steering assist under load or during tight turns
  • Steering-related warning message on dash (if equipped)
  • Possible hard steering at idle or during low-speed maneuvers

What to check

  • Read and record all stored and pending DTCs and freeze-frame data with a scan tool
  • Inspect pressure switch connector and wiring for corrosion, damage, pin pushed out, or bent pins
  • Check power steering fluid level and fluid condition (for hydraulic systems)
  • Back-probe and observe the pressure switch signal with a scan tool or multimeter while turning the steering from lock-to-lock
  • Perform wiggle test on harness to try to reproduce the fault
  • Check for related codes (powertrain, EPS module) that may indicate shared circuit issues

Signal parameters

  • Reference voltage: typically ~5.0 V supply to the switch (verify OEM spec)
  • Switch output: closed (pressure present) expected ~0–1 V; open (no pressure) expected ~4–5 V — verify against vehicle-specific values
  • Switch resistance: near 0 Ω when closed, very high/OL when open (verify with ohmmeter)
  • Signal should change state as steering load/pressure increases (observe live data)

Diagnostic algorithm

  1. Confirm DTC P1651 is current or pending. Note freeze-frame and related codes.
  2. Visually inspect pressure switch and harness for damage, corrosion, or fluid contamination. Repair any obvious issues and re-check.
  3. Verify power and ground to the switch: with key on, check reference (usually ~5V) and ground continuity to chassis ground/PCM using a digital multimeter. Repair poor connections.
  4. Back-probe the signal wire at the switch and observe voltage with engine running and while turning the steering wheel. Confirm the signal changes per expected behavior. If signal is stuck, suspect switch or wiring.
  5. Check switch resistance with connector disconnected. Operate steering (or apply pressure per OEM test) and verify open/closed resistance. Replace switch if out of spec.
  6. Perform continuity and short-to-power/short-to-ground tests on the harness between switch and PCM. Repair any short/open conditions.
  7. If wiring and switch test good and vehicle hydraulic pressure is normal, check for PCM/related module faults and perform module testing or reprogramming per manufacturer procedures.
  8. After repairs, clear DTCs and road-test to verify the code does not return.

Likely causes

  • Failed/shorted pressure switch
  • Damaged connector or corroded terminals at switch
  • Open or shorted signal/reference wire to PCM
  • Low hydraulic fluid level or pressure (mechanical issue)
  • Intermittent wiring fault (broken wire under insulation)

Fault status

⚠️ Status
Power Steering Pressure Switch Input Fault — PCM/ECM has detected an invalid, open, shorted, or out-of-range signal from the power steering pressure switch circuit.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0555 P0556 P1650 P0627
166

Browse 166 LINCOLN manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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